1. Field of the Invention
The invention relates to surge suppressors and, more particularly, to modular surge suppressor systems and modules for protecting electrical equipment connected to, for example, a residential alternating current (AC) power line, a telephone line, a cable television line, or a satellite receiver.
2. Background Information
Surge suppressors are voltage clamping devices, which are employed to protect a load, such as, for example, appliances, computers and other electrical equipment, from external surge sources. Such surge suppressors also protect such electrical equipment from internal surge sources (e.g., downstream of a panel board), which result from other equipment (e.g., resulting from motor switching, or operation of a switch to disconnect a load). The surge suppressors, thus, protect a load from both external disturbances (e.g., lightning voltage remnants) and internal disturbances (e.g., caused by other equipment).
Different kinds of surge suppressors have been developed for protecting alternating current (AC)-connected, telephone-connected, and cable-connected equipment. However, for effective operation, the surge suppressor must be connected as close as possible to the source of the disturbance. For a residential application, this location is the panel board, which houses the circuit breakers that distribute power throughout the residence. For new construction, the entrance for cable lines and telephone lines may be located relatively close to the panel board.
It is known to provide a series connection of a plurality of modular surge suppressors including a power distribution module followed by one or more coaxial connector based modules and one or more communication based modules. See, for example, U.S. Pat. No. Des. 382,855; U.S. Pat. Nos. 5,788,521; and 6,118,643.
In residential installations, the panel board typically includes a plurality of cables and wires, which may obstruct the mounting of a surge suppressor therein.
Under the UL Standard for Transient Voltage Surge Suppressors, UL 1449, second edition, the interrupt current rating of a surge suppression device must be greater than or equal to the interrupt current rating of the corresponding circuit breaker or panel board. This means that an explosive force, which occurs during a double continuous overvoltage, must be contained by the surge suppression device, in order to prevent fire and injury. During such an overvoltage, the voltage sensitive device (e.g., metal oxide varistor (MOV); gas tube; semiconductor clamping device) reacts violently as its impedance becomes lower in order to shunt the power line to ground. In this situation, ionized gas rapidly develops and is pressurized within the enclosure of the surge suppression device. Accordingly, such enclosure must be able to withstand that pressure. Although the corresponding circuit breaker will trip in order to interrupt the power circuit associated with the surge suppression device, the circuit breaker will typically not trip fast enough in order to prevent the failure of the voltage sensitive device.
Although residential circuit breakers and panel boards are typically rated at about 10 kA to about 22 kA interrupt current rating, the alternating current power source (e.g., the incoming AC power line to the residence) may have a relatively higher current rating. A fault condition may occur during an improper installation with an erroneous wiring connection of two power lines (e.g., 240 VAC line-to-line) to the line and neutral conductors of the surge suppression device (e.g., designed for operation at 120 VAC nominal). This is because the surge suppression device typically employs a voltage sensitive device (e.g., MOV) having a significantly lower voltage rating (e.g., 150 VAC). Although a relatively higher voltage MOV could be employed, that would increase the clamping voltage. Also, when there is a surge, the protected electrical equipment would be exposed to relatively higher voltages and, thus, may be damaged.
Another event that may trigger a catastrophic reaction in the surge suppression device is when the power line voltage significantly increases above its nominal value (e.g., due to capacitor switching; due to a lightening strike; due to a fault on the electric utility power line).
There is room for improvement in applications of a plurality of surge suppression devices.
There is also room for improvement in the response of surge suppression devices to catastrophic wiring faults and power line fault conditions.